The present invention concerns polymers suitable for use in making polymeric adsorbents and ion-exchange resins. More particularly, the invention concerns porous polymers having a unique cellular polymeric structure.
Ion-exchange resins are used by industry to separate chemical species from solutions containing them. Such resins are prepared by substituting various types of functional groups onto a crosslinked polymer matrix. The functional groups are capable of associating with chemical species so as to remove them from solution. Ion-exchange resins may be cation-, anion-, or chelate-exchange resins, depending on the choice of functional group substituted onto the copolymer matrix. The polymer matrix may also be used in preparing polymeric adsorbents, such as the post-crosslinked adsorbent resins disclosed in U.S. Pat. No. 4,950,332.
The polymer matrix is typically in spheroidal bead form and is generally prepared by suspension polymerization of a finely divided organic phase within a continuous suspending medium. The organic phase comprises monovinylidene monomers like styrene, polyvinylidene monomers like divinylbenzene and a free-radical polymerization initiator. The copolymer beads produced may be microporous, i.e., gel in character, or macroporous, depending upon whether a phase-separating diluent is added to the organic phase. The term "macroporous" refers to the fact that the copolymer has both macropores and and micropores. The terms "microporous", "gel", and "macroporous" are well known in the art and generally describe the nature of the copolymer bead porosity. Microporous copolymer beads have pore sizes on the order of about 50 Angstroms (.ANG.) or less, while macroporous copolymer beads have macropores of about 100 .ANG. or greater. Gel and macroporous copolymer beads, as well as their preparation, are further discussed in U.S. Pat. No. 4,256,840.
Adsorbent resins based on a post-crosslinked, gel copolymer matrix can be difficult to manufacture as the gel copolymer is, in many instances, susceptible to breakage during the post-crosslinking step employed. Conventional macroporous copolymers generally have better strength relative to gel copolymers and, as a result, are less susceptible to such breakage. However, adsorbent resins derived from such conventional macroporous copolymers may have less adsorption capacity relative to the gel adsorbent resin due to a higher degree of porosity, or void space.
As can be seen, it is desirable to develop a polymerization process for producing copolymer beads which have sufficient strength to resist breakage and also capable of being converted into resins with sufficient capacity. Such copolymer beads would be advantageous for use in preparing polymeric adsorbents, as well as ion-exchange resins.